Search for x-ray induced decay of the 31-yr isomer of 178Hf at low x-ray energies

Upper limits for the energy-integrated cross section for the decay of the 31-yr ¹⁷⁸Hf isomer, induced by x-ray irradiation, are extended to lower x-ray energies than we reported previously. Over the range of incident x-ray energies 6<E_x (keV)<20, we report the energy-integrated cross section as less than 1×10^-26 cm² keV, with less stringent limits set down to 4 keV. These limits are at least 3 orders of magnitude below values for which enhancements to the isomer decay rate have been reported by other workers.